Many organizations and enterprises provide computerized directory services for locating members of the organization and for obtaining information about the members. Typically, a user of an employee locator or people-finder application program enters a portion of the name of the sought-after individual, or other relevant information, into a search field. The user then initiates the search by activating a graphical user interface button displayed for that purpose. The application program then generates a query expression based on the user-supplied input and issues the query to a directory system. Within this directory system, the information sought for by the query may reside across multiple heterogeneous data stores (or repositories).
Directory systems operating over heterogeneous repositories generally provide an application program interface (API) for searching the virtual repository (i.e., an abstraction of the multiple heterogeneous data stores and instances). Often, however, the client application bears the complexity of the query construction. For instance, the client application may need to conform the query expression to a proprietary query object model that is cumbersome and constrained by query-construction artifacts, such as an inability to express precedence of evaluation with parentheses or to specify logical OR operations. In such systems, constructing simple queries can involve an inordinate amount of program code.
Moreover, programmers often need to specify the locations in the data stores, (i.e., the client application needs to know the table and column names of the various repositories, must repeat the query across the horizontal repositories, and then specify the join conditions against the vertical repositories). Thus, the client application needs to be attribute-location aware, issue multiple queries, and manually join the data returned by the queries. Other directory system implementations cannot work with heterogeneous data stores (e.g., LDAP—Lightweight Directory Access Protocol) or support horizontal and vertical federation of query results, and still other systems are unable to accommodate dynamic definition of attributes.